1. Field of the Invention
The present invention relates to a setting tool for driving fastening elements in a constructional component and including a piston guide having a hollow chamber, a setting piston axially displaceable in the hollow chamber and having a piston head and a piston stem adjoining the piston head, a bolt guide adjoining the piston guide in a setting direction of the setting tool, and a piston stop device for braking the setting piston, located at an end region of the hollow chamber adjacent to the bolt guide, and having a stop element for the setting piston.
2. Description of the Prior Art
Setting tools of the type described above can be operated with solid, gaseous, or fluid fuels or with compressed air. With combustion-operated setting tool, the setting piston is driven by combustion gases. The setting tool can drive fastening elements such as, e.g., nails or bolts in a constructional component.
In setting tools such as disclosed in German Publication DE 39 30 592 A1, the setting piston is displaceably arranged in a piston guide axially displaceable in a housing sleeve of the setting tool. For initiating a setting process, the setting tool has to be pressed against a constructional component so that the piston guide is pushed into the housing sleeve. In order to reduce the piston energy at faulty settings or to reduce an excessive setting energy, there is provided, in the front portion of the piston guide, in the end region of the piston guide adjacent to the bolt guide, an elastic annular member for braking the setting piston.
The drawback of the known setting tool consists in that when the wear of the elastic annular member is too large and the wear is not recognized, essential and expensive tool components can be damaged. Further, the piston collar that impacts the annular member, should have as large a diameter as possible to prevent a premature damage of the annular member. This increases the weight of the setting tool. On the other hand, because of the elasticity of the annular member, the setting piston rebounds after impacting the annular member, and this leads, in particular at a high setting energy, to undesirable second blows with the setting piston.
German patent DE 196 17 671 C1, from which the present invention proceeds, discloses a powder charge-operated bolt setting tool with a setting piston displaceable in a guide bore. The setting piston has a piston head and a piston stem, with the piston head forming, at its side adjacent to the piston stem, a conical section. A conical receptacle, which is provided at the mouth-side end of the guide part, is arranged opposite the conical section formed by the piston head. At a faulty setting or an excessive setting energy, the conical section of the piston head passes into the conical receptacle. A damping disc, which is arranged behind the conical receptacle in the setting direction, dampens the impact of the piston.
In the setting tool of the above-mentioned German patent, an increased wear of the elastic damping disc, which takes place in the setting tool of DE 39 30 592 A1, is prevented. However, in the setting tool of the German patent, the other drawback of DE 39 30 592 A1, namely, rebound of the setting piston, leading to secondary blows, remains.
U.S. Pat. No. 4,824,003 discloses a setting tool in which between the piston guide and the bolt guide, there are provided a first rigid ring and an elastic ring arranged one after another. In the elastic ring, there is provided a further, more rigid ring that limits the stroke of the first rigid ring. The first rigid ring has a through-guide for the piston stem tapering in the setting direction. The piston collar surface adjacent to the first rigid ring is formed as a conical surface, with the profiles of the conical surface of the through-guide and the conical surface of the piston collar complementing each other.
The setting tool of the U.S. patent has the same drawback as the setting tool of the German patent. Here, likewise, possible rebounds of the setting piston can lead to the secondary blows.
Accordingly, an object of the present invention is to provide a setting tool of the type discussed above in which the foregoing drawbacks are eliminated, and the rebound speed of the setting piston is reduced to a minimum.